Appliance of Science: what happens when it feels like you're falling as you fall asleep

You’ve had a long day, you finally get to bed and just as you drift off to sleep… bam! You experience a shock sensation like you are falling in mid-air and it is enough to jolt you back awake again. Sound familiar? It probably does, as at least seventy percent of us experience this sensation at some stage, but why do we feel like we are falling as we fall asleep?

What a jerk

This phenomenon is most commonly called a hypnic jerk, but it goes by other names too, like hynogogic jerk or a sleep start. Hypnic jerks are brief, involuntary muscle twitches, referred to as myoclonus. These muscle twitches are most commonly in our leg muscles but can occur in any of our muscles, sometimes the whole body jerks in this way.

The muscle twitches associated with hiccupping are also mycoclonic.

What causes these falling sensations?

The ancient Greeks thought these hypnic jerks were just the dream demons (Oneiroi) playing tricks on us mere mortals. While we have moved on in our understanding of what these involuntary movements are and why they happen, we still have a long way to go. There are, of course, a number of theories as to why these falling feelings occur.

In order for us to fall asleep the body, and mind, need to switch off certain functions, control systems and pathways. We switch off parts of our sensory system as we advance through the stages of sleep. One example of this is a region deep within the brain, known as the thalamus.

The thalamus acts act as a sensory relay station; almost all sensory information from the body (with the exception of smell) passes through the thalamus before moving on to its destination within other areas of the brain. In order to fall asleep we must inhibit this relay system.

When the thalamus is inhibited the body may become disorientated as the sensory feedback has been switched off. Without this our bodies may feel weightless and that could be what causes those feelings of falling into emptiness (free fall). Naturally this sensation suggests immediate threat to the body so the hypnic jerk is triggered to knock the person back into consciousness.

There are other theories that suggest this phenomenon has an evolutionary link. Our ancestors were vulnerable when they slept so the hypnic jerk may have been a way to awaken them one more time, to check the safety of their surroundings, before fully succumbing to sleep.

Is it dangerous?

During hypnic jerks the body may experience an increase in heart beat, breathing, sweating or a sense of shock. None of these are usually of serious concern to the health of the person experiencing them.

A small number of people can experience this sensation frequently and repeatedly throughout the night, causing a significant disturbance in their sleeping pattern. This can lead to health issues associated with sleep deprivation. For the majority of people though, these falling sensations have little to no impact on our health or overall sleep quality.

Can it be prevented?

Anyone can experience hypnic jerks at any time. There are however possible triggers that can bring on these sensations in some people; These triggers include stimulants like caffeine or nicotine, extreme fatigue or sleep deprivation, physical or mental stress or certain drugs. If hypnic jerks are becoming an issue it is worth removing these stimulants, if possible, in the hope that there is no falling, as you fall asleep.